How to edit data in CSV with equations to convert to new values?

Question

I've been trying to find a solution. But most of all, I found only a few lines of csv editing. But the data that I have and have to solve consists of thousands of lines. 

The data that I use is the value from the sensor-read. but it comes out in voltage. I need to convert it by using equations (which I already have).But I don't know how to use it to edit with many row in csv.

Data sample

ID	Voltage
1	1979
2	1978
...	...
49999	1976
50000	1976

I want to create new column and convert value from old existing column to new column and export to new csv file. Is there any way that can solve it?

I don't know if I should give an example of the equation. But let's just put it together. My equations will be like

Moisture = 100 - ( 0.01 x Voltage )

Here is sample of csv that I want.

ID	Voltage	Moisture
1	1979	80
2	1978	80
...	...	...
49999	1976	81
50000	1976	81

Answer 1

load the csv into a dataframe, this is done easily with pandas

import pandas as pd

df = pd.read_csv('file_path.csv')

then you can create a new column and assign it a value base of existing columns

df['Moisture'] = 100 - (df['Voltage'] * 0.01)

then you can save the dataframe back to a csv

df.to_csv('file_path.csv', index=False)

Answer 2

You can use csv module for that. You can read data from csv into dictionaries and then just update those dictionaries and write it back. Something like this:

import csv

old_data = list()
with open('data.csv', newline='') as f:
    old_data = list(csv.DictReader(f))
    for d in old_data:
        d['Moisture'] = 100 - (0.01 * d['Voltage'])

    with open('new_data.csv', mode='w') as csv_file:
        writer = csv.DictWriter(csv_file,
                                    fieldnames=['ID', 'Voltage', 'Moisture'],
                                    lineterminator='\n')
       writer.writeheader()
       writer.writerows(old_data)

Answer 3

The following approach just uses the built in CSV library and would work on any file size:

import csv

with open('input.csv') as f_input, open('output.csv', 'w', newline='') as f_output:
    csv_input = csv.reader(f_input)
    csv_output = csv.writer(f_output)
    csv_output.writerow([*next(csv_input), 'Moisture'])
    
    for id, voltage in csv_input:
        voltage = float(voltage)
        csv_output.writerow([id, voltage, f"{100 - ( 0.01 * voltage ):.1f}"])          # Use .0f if 80 needed (not 80.1)